All major trailer makers earn IIHS award for good underride protection

Seven years after IIHS found serious shortcomings in the rear underride guards of most semitrailers, the eight largest North American manufacturers are now making rear guards capable of preventing deadly underride in a range of scenarios.

September 27, 2018

Seven years after the Insurance Institute for Highway Safety found serious shortcomings in the rear underride guards of most semitrailers, the eight largest North American manufacturers are now making rear guards capable of preventing deadly underride in a range of scenarios. All eight companies earn the IIHS Toughguard award.

The companies — Great Dane LLC, Hyundai Translead, Manac Inc., Stoughton Trailers LLC, Strick Trailers LLC, Utility Trailer Manufacturing Co., Vanguard National Trailer Corp. and Wabash National Corp. — represent approximately 80 percent of the trailers on the road in the U.S. All but one of them, Manac, had to make changes to its underride guard before they were able to pass the three IIHS tests.

"We're pleased that all the major manufacturers responded positively to our underride tests," says David Zuby, IIHS chief research officer. "By improving their guards, these companies have demonstrated a commitment to the safety of passenger vehicle occupants who share the road with their trailers."

Underride occurs when a passenger vehicle slides under a larger vehicle during a crash. This usually causes severe intrusion into the passenger vehicle's occupant space and is often deadly. Rear underride guards are metal bumpers that hang from the backs of trailers to prevent underride in a rear impact.

Trailers on U.S. roads must have underride guards that meet federal safety standards, and guards from the major manufacturers also meet a more stringent Canadian regulation. However, IIHS research showed that even guards that met these requirements could buckle or break off in a crash. The Institute's testing program prompted engineering improvements that went further. Some of the manufacturers have made the improved guards standard on all new trailers, while in other cases they are optional.

Trailers that qualify for the Toughguard award have rear guards that prevent underride of a midsize car in three test modes — full-width, 50 percent overlap and 30 percent overlap. In each configuration, a typical midsize car travels at 35 mph toward the back of a parked semitrailer. In the full-width test, which all trailers were able to pass in the initial round of testing, the car strikes the center of the guard head-on. In the 50 percent overlap, which all but one trailer passed initially, half of the car's front end strikes the guard. In the 30 percent overlap, the toughest evaluation, 30 percent of the car's front strikes the corner of the trailer.

Manac was the only manufacturer whose guard prevented underride in the 30 percent overlap test during the first round of testing. All the other companies made updates to their guards and then requested retests. By the time IIHS announced the Toughguard award last year, 5 of the 8 guards met the criteria.

Since then, Hyundai Translead and Utility have earned the award. Strick now joins them, thanks to a new underride guard that completes the industry's effort to improve protection against rear underride.

Strick's new guard is the company's second attempt at a better design and includes additional vertical supports at the edges — a strategy that was also employed successfully by other manufacturers.

"We were pleased that Strick didn't give up on better protection when their first modification didn't work out," Zuby says.

In 2016, 424 of the 2,056 passenger vehicle occupants killed in large truck crashes died when their vehicles struck the rear of a large truck. It's not known how many of these were underride crashes. A 2010 IIHS analysis of a small sample of fatal crashes involving the rear of a truck found that 82 percent involved underride.

Rear guards address just one part of the underride problem. Side underride is also a danger, but there are no requirements in the U.S. for side guards that protect passenger vehicle occupants. IIHS has tested an aftermarket side guard called the AngelWing and produced by Airflow Deflector Inc. It successfully prevented underride when a Chevrolet Malibu struck the side of a trailer at 35 mph and 40 mph in two separate tests.

IIHS has been studying underride crashes for more than 40 years, including crash tests in the mid-1970s demonstrating how then-current guards were too flimsy to prevent underride even in full-width tests.

The Highway Loss Data Institute (HLDI) shares and supports this mission through scientific studies of insurance data representing the human and economic losses resulting from the ownership and operation of different types of vehicles and by publishing insurance loss results by vehicle make and model.